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In vivo measurement of bending stiffness in fracture healing.

Hente R, Cordey J, Perren SM - Biomed Eng Online (2003)

Bottom Line: Measurement of stiffness data over time revealed a significant logarithmic increase between the third and seventh weeks, whereby the logarithmic rate of change among sheep was similar, but started from different levels.Comparative measurements showed that early individual changes between the third and fourth weeks can be used as a predictor of bending stiffness at seven weeks (r = 0.928) and at ten weeks (r = 0.710).Bending stiffness can be measured precisely, with less error in the case of pin loosening.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Regensburg, Trauma Centre Regensburg, Franz-Josef-Strauss-Allee 11, D-93042 Regensburg, Germany. reiner.hente@klinik.uni-regensburg.de

ABSTRACT

Background: Measurement of the bending stiffness a healing fracture represents a valid variable in the assessment of fracture healing. However, currently available methods typically have high measurement errors, even for mild pin loosening. Furthermore, these methods cannot provide actual values of bending stiffness, which precludes comparisons among individual fractures. Thus, even today, little information is available with regards to the fracture healing pattern with respect to actual values of bending stiffness. Our goals were, therefore: to develop a measurement device that would allow accurate and sensitive measurement of bending stiffness, even in the presence of mild pin loosening; to describe the course of healing in individual fractures; and help to evaluate whether the individual pattern of bending stiffness can be predicted at an early stage of healing.

Methods: A new measurement device has been developed to precisely measure the bending stiffness of the healing fracture by simulating four-point-bending. The system was calibrated on aluminum models and intact tibiae. The influence of pin loosening on measurement error was evaluated. The system was tested at weekly intervals in an animal experiment to determine the actual bending stiffness of the fracture. Transverse fractures were created in the right tibia of twelve sheep, and then stabilized with an external fixator. At ten weeks, bending stiffness of the tibiae were determined in a four-point-bending test device to validate the in-vivo-measurement data.

Results: In-vivo bending stiffness can be measured accurately and sensitive, even in the early phase of callus healing. Up to a bending stiffness of 10 Nm/degree, measurement error was below 3.4% for one pin loose, and below 29.3% for four pins loose, respectively. Measurement of stiffness data over time revealed a significant logarithmic increase between the third and seventh weeks, whereby the logarithmic rate of change among sheep was similar, but started from different levels. Comparative measurements showed that early individual changes between the third and fourth weeks can be used as a predictor of bending stiffness at seven weeks (r = 0.928) and at ten weeks (r = 0.710).

Conclusion: Bending stiffness can be measured precisely, with less error in the case of pin loosening. Prediction of the future healing course of the individual fracture can be assessed by changes from the third to the fourth week, with differences in stiffness levels. Therefore, the initial status of the fracture seems to have a high impact on the individual healing course.

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Sequential stiffness measurement. Increase of callus bending stiffness versus healing time of all sheep. From the third week on, fracture stiffness is obviously increasing. All stiffness values at ten weeks were obtained from four-point-bending tests in a material testing machine. Note that the curves of the in-vivo-measurements closely correspond to the more accurate ex vivo measurements obtained from the 4-point-bending test. In those sheep where progressive pin loosening was evident, the data points were omitted.
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Figure 7: Sequential stiffness measurement. Increase of callus bending stiffness versus healing time of all sheep. From the third week on, fracture stiffness is obviously increasing. All stiffness values at ten weeks were obtained from four-point-bending tests in a material testing machine. Note that the curves of the in-vivo-measurements closely correspond to the more accurate ex vivo measurements obtained from the 4-point-bending test. In those sheep where progressive pin loosening was evident, the data points were omitted.

Mentions: Weekly in-vivo-measurement of bending stiffness in all sheep showed an increase in bending stiffness from the second week onwards (Fig. 7). The increase in bending stiffness at the third week varied among individual sheep (Table 2). Each sheep had its own characteristic curve, representing its individual healing pathway. In none of the sheep could any interference of this healing course with respect to mechanical changes be observed. All curves showed a continual increase in bending stiffness up to the tenth week. At the end of the observation time, the difference in actual bending stiffness was large, ranging from 13.3 Nm/degree up to 43.1 Nm/degree. Logarithmic transformation of the stiffness data showed a linear increase of fracture stiffness between the third and the seventh weeks, whereas data values at the second week did not yet give predictive information on the course of healing (Fig. 8). Testing of the logarithmically transformed linearity data (linear regression test) showed a high correlation coefficient for all sheep (mean ± standard deviation: r = 0.950 ± 0.037, Table 3). Therefore, the assumption of logarithmic stiffness increase can be confirmed. The healing rates shown by the fitted lines of the transformed data were tested by using the gradient of the best fit lines in relation to the measured stiffness at 7 and 10 weeks, but did not show a significant linear relationship (Table 4). The slope of the fitted line of the transformed data can therefore not be assumed to be an early indicator for healing. The slopes of the transformed data between the third and the seventh weeks rather tend to be parallel and converge after the sixth week (Fig. 8). However, the intercept of the fitted line of the logarithmic data reveals a significant predictive value of future bending stiffness (Tab. 4). In conclusion, the rate of healing in the logarithmic data representation among individual sheep, was similar, but started at different levels from the third week on.


In vivo measurement of bending stiffness in fracture healing.

Hente R, Cordey J, Perren SM - Biomed Eng Online (2003)

Sequential stiffness measurement. Increase of callus bending stiffness versus healing time of all sheep. From the third week on, fracture stiffness is obviously increasing. All stiffness values at ten weeks were obtained from four-point-bending tests in a material testing machine. Note that the curves of the in-vivo-measurements closely correspond to the more accurate ex vivo measurements obtained from the 4-point-bending test. In those sheep where progressive pin loosening was evident, the data points were omitted.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC153498&req=5

Figure 7: Sequential stiffness measurement. Increase of callus bending stiffness versus healing time of all sheep. From the third week on, fracture stiffness is obviously increasing. All stiffness values at ten weeks were obtained from four-point-bending tests in a material testing machine. Note that the curves of the in-vivo-measurements closely correspond to the more accurate ex vivo measurements obtained from the 4-point-bending test. In those sheep where progressive pin loosening was evident, the data points were omitted.
Mentions: Weekly in-vivo-measurement of bending stiffness in all sheep showed an increase in bending stiffness from the second week onwards (Fig. 7). The increase in bending stiffness at the third week varied among individual sheep (Table 2). Each sheep had its own characteristic curve, representing its individual healing pathway. In none of the sheep could any interference of this healing course with respect to mechanical changes be observed. All curves showed a continual increase in bending stiffness up to the tenth week. At the end of the observation time, the difference in actual bending stiffness was large, ranging from 13.3 Nm/degree up to 43.1 Nm/degree. Logarithmic transformation of the stiffness data showed a linear increase of fracture stiffness between the third and the seventh weeks, whereas data values at the second week did not yet give predictive information on the course of healing (Fig. 8). Testing of the logarithmically transformed linearity data (linear regression test) showed a high correlation coefficient for all sheep (mean ± standard deviation: r = 0.950 ± 0.037, Table 3). Therefore, the assumption of logarithmic stiffness increase can be confirmed. The healing rates shown by the fitted lines of the transformed data were tested by using the gradient of the best fit lines in relation to the measured stiffness at 7 and 10 weeks, but did not show a significant linear relationship (Table 4). The slope of the fitted line of the transformed data can therefore not be assumed to be an early indicator for healing. The slopes of the transformed data between the third and the seventh weeks rather tend to be parallel and converge after the sixth week (Fig. 8). However, the intercept of the fitted line of the logarithmic data reveals a significant predictive value of future bending stiffness (Tab. 4). In conclusion, the rate of healing in the logarithmic data representation among individual sheep, was similar, but started at different levels from the third week on.

Bottom Line: Measurement of stiffness data over time revealed a significant logarithmic increase between the third and seventh weeks, whereby the logarithmic rate of change among sheep was similar, but started from different levels.Comparative measurements showed that early individual changes between the third and fourth weeks can be used as a predictor of bending stiffness at seven weeks (r = 0.928) and at ten weeks (r = 0.710).Bending stiffness can be measured precisely, with less error in the case of pin loosening.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Regensburg, Trauma Centre Regensburg, Franz-Josef-Strauss-Allee 11, D-93042 Regensburg, Germany. reiner.hente@klinik.uni-regensburg.de

ABSTRACT

Background: Measurement of the bending stiffness a healing fracture represents a valid variable in the assessment of fracture healing. However, currently available methods typically have high measurement errors, even for mild pin loosening. Furthermore, these methods cannot provide actual values of bending stiffness, which precludes comparisons among individual fractures. Thus, even today, little information is available with regards to the fracture healing pattern with respect to actual values of bending stiffness. Our goals were, therefore: to develop a measurement device that would allow accurate and sensitive measurement of bending stiffness, even in the presence of mild pin loosening; to describe the course of healing in individual fractures; and help to evaluate whether the individual pattern of bending stiffness can be predicted at an early stage of healing.

Methods: A new measurement device has been developed to precisely measure the bending stiffness of the healing fracture by simulating four-point-bending. The system was calibrated on aluminum models and intact tibiae. The influence of pin loosening on measurement error was evaluated. The system was tested at weekly intervals in an animal experiment to determine the actual bending stiffness of the fracture. Transverse fractures were created in the right tibia of twelve sheep, and then stabilized with an external fixator. At ten weeks, bending stiffness of the tibiae were determined in a four-point-bending test device to validate the in-vivo-measurement data.

Results: In-vivo bending stiffness can be measured accurately and sensitive, even in the early phase of callus healing. Up to a bending stiffness of 10 Nm/degree, measurement error was below 3.4% for one pin loose, and below 29.3% for four pins loose, respectively. Measurement of stiffness data over time revealed a significant logarithmic increase between the third and seventh weeks, whereby the logarithmic rate of change among sheep was similar, but started from different levels. Comparative measurements showed that early individual changes between the third and fourth weeks can be used as a predictor of bending stiffness at seven weeks (r = 0.928) and at ten weeks (r = 0.710).

Conclusion: Bending stiffness can be measured precisely, with less error in the case of pin loosening. Prediction of the future healing course of the individual fracture can be assessed by changes from the third to the fourth week, with differences in stiffness levels. Therefore, the initial status of the fracture seems to have a high impact on the individual healing course.

Show MeSH
Related in: MedlinePlus